An end effector that employs a multiple bar linkage is known. One reason for using a structure of this type is to enable the jaws of the end effector to be closed in a more parallel manner. However, present end effectors of this type are not effective in providing a uniform grasping action as there is excessive lateral action upon closing the end effector. With existing jaw constructions the jaws travel, upon closing, to provide a significant undesired sheering action where the end effector jaws engage tissue or a vessel.
A rudimentary form of a grasper may be considered as consisting of a pair of jaws with a single pivot point and act like a pair of needle nose pliers. This type of closing action puts immense pressure on tissue portions nearest the apex of the jaws with a squeezing action forcing soft tissue outwards towards the ends of the jaws. This type of end effector can cause severe damage to delicate soft tissue.
An alternative style of jaws is a parallel jaws mechanism such as shown in FIGS. 2-7. This type of jaw mechanism exerts a more even top to bottom clamping pressure on soft tissue but still has a disadvantage in that the top, moveable jaw has a horizontal travel component that can effect a tearing action on soft tissue such as veins as the jaws are closed upon them. The end effector construction shown in FIGS. 2-7 herein employs a multiple bar linkage for operating the end effector.
Reference is now made to FIGS. 2-4, which illustrates the fixed jaw 146 and related movable jaw 144. The end effector 16 includes a main body portion 154 of the fixed jaw 146 that is affixed to the distal end of distal bending member 20. A protective sheath 98 may be disposed about the distal bendable member 20 to prevents bodily fluids from entering cavities in the distal bending member. A channel 147 is formed in the main body 154 for receiving the moveable jaw 144 therein. The moveable jaw 144 is hinged to the main body 154 by means of two links 156 and 158 which are attached to fixed pivot points on both the moveable and fixed jaws. As illustrated in FIGS. 2 and 3, the upper ends of links 156, 158 extend into slot 149 formed in the moveable jaw 144 and are joined by pivot pins 162, 164 to bores 163, 165 in the jaw 144. The lower ends of links 156,158 extend into slot 148 formed at the bottom of channel 147 and are joined by pivot pins 166,168 to bores 167,169 in the main body 154. This fixed point linkage arrangement results in significant lateral action as the upper jaw 144 rocks back and forth on links 156 and 158 as can be seen in the sequence views described in FIGS. 4-7.
The actuation cable 38 is attached at its' proximal end to a slider/ratchet mechanism (not shown) in the handle of a surgical tool that, instead of imparting a proximal pulling motion to cable 38 when the jaw actuation lever is squeezed, imparts a distal pushing motion to cable 38 when the jaw actuation lever is squeezed. The distal end of cable 38 is fixed to yoke 138 which is slidably mounted in the main body 154. The yoke has tubular boss 139 which rides in guide/bore 155 in the main body 154. The boss 139 is firmly fixed on the end of cable 38 and is free to slide proximally/distally in the bore 155. The yoke 138 is coupled with an arm extension 160 at the proximal end of moveable jaw 144 by pin 142. The extension arm 160 is disposed angularly to the main longitudinal axis of the movable jaw 144. See, for example, FIGS. 3-5 where the extension arm 160 has an elongated slot 161. The pin 142 is force fit in bores 143 in the yoke 138 and passes through, and is free to slide vertically in, the slot 161 in the extension arm 160. The extension arm 160 thus is free to slide vertically in relation to the yoke 138 so as to accommodate the vertical movements of the moveable jaw as it opens and closes in response to the push/pull action of the cable 38. The jaws 144, 146 have opposing serrations 170 for enhanced the gripping of tissue.
FIGS. 4-7 show a sequence of action as the jaws clamp down on an object such as a the illustrated vein V. FIG. 4 shows the moveable jaw 144 in a fully open position about to close down on the vein V. In this position the tip 174 of the movable jaw 144 is situated a maximum distance DMAX proximally from the tip 176 of the fixed jaw 146. As the jaw actuation lever (not shown) is squeezed, the cable 38 is urged distally (arrow 172) and the serrations 170 on jaw 144 make contact with a top contact point TCP on vein V while the serrations 170 on jaw 146 make contact with bottom contact point BCP on vein V as shown in FIG. 5. As the moveable jaw 144 closes down upon the vein (arrow 178) a rolling action is imparted to the vein V as indicated by the vector of arrow 178. By the time the jaws have closed to the extent illustrated in FIG. 6 the top contact point TCP has traveled an average distance DAVG in relation to the bottom contact point BCP. This rolling motion in conjunction with the serrations 170 can cause a significant tearing action in any soft tissue and is a major drawback to this type of jaw actuation mechanism. The distance DAVG may be slightly less than DMAX due to the offset of TCP and BCP according to how far distal or proximal they occur along the length of the jaw serrations in relation to the size of the tissue grabbed. FIG. 7 shows the jaws fully closed without any tissue present.
Accordingly, it is an object of the present invention to provide an improved end effector construction, and in particular one that has the jaws of the end effector close without any substantial lateral motion between the jaws.
Another object of the present invention is to provide an improved end effector construction with absolute minimum lateral motion between the jaws, and with a structure that is relatively simple, operates effectively and can be manufactured relatively inexpensively.